1. Field of the Invention
The present invention relates to a rotating electrical machine, specifically, a cooling structure for cooling a stator core of the rotating electrical machine, and to a method of manufacturing the cooling structure.
2. Description of the Related Art
Hitherto, as a method of cooling a stator core, there is known a method of causing cooling water, oil, or the like to flow between an outer periphery of a tubular member (hereinafter referred to as “stator frame”) for holding a stator and a tubular member (hereinafter referred to as “motor case”) having an inner diameter with a predetermined space with respect to the outer side of the stator frame. Further, sealing for preventing leakage of cooling water is generally carried out by sandwiching elastic members such as O-rings between an outer peripheral member and an inner peripheral member (for example, see Japanese Patent No. 5136069 and Japanese Patent Application Laid-open No. 2009-247085).
Hitherto, there has been known a structure as described in, for example, Japanese Patent No. 5136069 in which a space is formed between the stator frame for holding the stator core and the motor case for accommodating the stator frame therein, and cooling water is caused to flow therebetween to cool the stator frame. Further, the airtightness of a cooling passage is secured by elastic members (O-rings) arranged with a predetermined distance in a rotary shaft direction of the rotating electrical machine. The elastic members seal the outer periphery of the stator frame and the inner periphery of the motor case around the entire circumference. The O-ring serving as the elastic member extends around the entire circumference of the rotating electrical machine.
In order to secure the airtightness in this structure, the squeeze rate of the O-ring is required to be appropriately managed. Therefore, high accuracy is required in processing of the outer periphery of the stator frame and the inner periphery of the motor case and in assembly of those members, which leads to a high-cost structure in manufacture. Further, when the O-ring, which is generally manufactured through metal molding, increases in size, production efficiency reduces to increase the cost. That is, when the O-ring increases in size, a larger mold is required, and only a single O-ring can be manufactured at once. In particular, when the above-mentioned method is applied to a large-sized motor such as an automobile motor, the cost of the O-ring dramatically increases.
Further, in order to install the O-ring, it is necessary to subject the outer periphery of the stator frame or the inner periphery of the motor case to processing of forming a groove for installing the O-ring. The groove for installing the O-ring requires high accuracy and low surface roughness so as to hold the O-ring and secure the airtightness. In general, machining is carried out. Therefore, processing difficulty is high, which leads to increase in cost.
Further, because the groove for installing the O-ring is required, the stator frame or the motor case requires a thickness that enables the processing. As a result, the weight increases, and further the processing method is limited. Further, processing methods such as sheet metal forming of a thin sheet that can be generally manufactured at low cost and high accuracy through metal component molding cannot be used. In general, a blank is formed through forging and casting, which are difficult to secure accuracy, and most part of the blank is subjected to cutting.
Further, the stator core is press-fitted into the stator frame. The stator frame has high rigidity, and hence the core loss of the stator increases due to the exceeded press-fit force, which eventually causes reduction in motor performance.